Topic content:
Chemistry is closely related to production and life. The following mistakes are made ()
A. Add soapy water to soften hard water
B. Eating qualified iodized salt to prevent thyroid diseases
C. Draw and ignite to identify cotton fiber and synthetic fiber
D. Fireworks are prohibited and ventilation is maintained to prevent gas explosion in the mine
Best answer:
A、 Soap water can identify soft water and hard water, and can not reduce the hardness of water, so it is wrong to say;
B、 It is correct to say that iodized salt can be used to prevent thyroid diseases;
C、 After the wool and synthetic fiber are burned and cooled, the wool is easy to twist into ash, and the synthetic fiber becomes a very hard glass ball, which can be identified from the hand feel, so C is correct;
D、 Because methane is flammable, combustible gas may explode in case of open fire, static electricity or electric spark after mixing with air or oxygen to reach the explosion limit; In order to prevent the "gas" explosion accident in the coal mine, mine ventilation can reduce the gas concentration, prevent the gas concentration from reaching the explosion limit, take away heat, and reduce the ambient temperature. The pyrotechnic control is to avoid gas explosion if there is no fire when the gas concentration is within the explosion limit, so the statement is correct
Therefore, A
Answer analysis:
There is no explanation for this question
Test core:
The existence form of elements in human body:
① Carbon, hydrogen, oxygen and nitrogen mainly exist in the form of water, sugar, protein, vitamins and fat.
② Other elements mainly exist in aqueous solution in the form of inorganic salts.
③ Calcium element mainly exists in the form of hydroxycalcium phosphate [Ca10 (PO4) 6 (OH) 2] crystal.